[ruby-core:75350] [Ruby trunk Bug#9569] SecureRandom should try /dev/urandom first

Issue #9569 has been updated by Akira Tanaka.


I think switching OpenSSL to getrandom() is possible if the performance is acceptable.
The man page for getrandom(),
http://man7.org/linux/man-pages/man2/getrandom.2.html
doesn't discourage non-seed cryptgraphic purposes.

OpenBSD's getentropy() has limitation on buffer size: 256 bytes.
http://man.openbsd.org/OpenBSD-current/man2/getentropy.2
Some gems use SecureRandom.random_bytes(more-than-256).
So, making SecureRandom.random_bytes as single getentropy() invocation
causes incompatibility.

arc4random may be possible.
However, I'm not sure that arc4random is preferable over OpenSSL.



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Bug #9569: SecureRandom should try /dev/urandom first
https://bugs.ruby-lang.org/issues/9569#change-58478

* Author: Corey Csuhta
* Status: Rejected
* Priority: Normal
* Assignee: ruby-core
* ruby -v: 
* Backport: 
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Right now, `SecureRandom.random_bytes` tries to detect an OpenSSL to use before it tries to detect `/dev/urandom`. I think it should be the other way around. In both cases, you just need random bytes to unpack, so SecureRandom could skip the middleman (and [second point of failure](http://sockpuppet.org/blog/2014/02/25/safely-generate-random-numbers/)) and just talk to `/dev/urandom` directly if it's available.

Is this a case of just re-ordering the two code chunks so that `/dev/urandom` is tried first?

Relevant lines: https://github.com/ruby/ruby/blob/trunk/lib/securerandom.rb#L59-L90



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